The invention relates to a method of laying conduits in the ground without the need to excavate the ground significantly.
Typically, the invention is applied to the connection of a buried section of main conduit (such as a pressurized fuel-gas conduit) to a secondary distribution conduit, for example, to a building.
Every residential or office building has a large number of underground conduits which supply and take away, for example, water, gas, electrical current, etc.
In the past, particularly in order to lay conduits of this type in the ground, trenches were excavated, the conduits were laid therein, and the trenches were then filled in again.
This is expensive, dangerous and impractical.
For this reason, it is already known to lay conduits such as pipes without the need to excavate trenches for the entire length of the conduit.
Thus, a drilling machine has already been used for driving a train of rods constituted by a large number of drilling bars or rods disposed end to end (for example screwed) and each several meters long into the ground, from the surface, along an oblique path. In this case, the direction of penetration (that is, of the drilling head which is disposed at the front end of the train of rods) can be regulated quite well so that the drilling first takes place obliquely downwards until the required depth is reached and then continues in a substantially horizontal direction.
After the drilling has been carried out and before the train of rods is removed, the conduit to be inserted (for example, a slightly flexible steel or plastic pipe) is fixed to the front end of the train of rods with the aid of a special device and the conduit to be laid is inserted in the drilling hole already in place with the aid of this device, and by progressive rearward movement (extraction) of the train of rods.
This method is used in particular for laying conduits over very long sections, for example, of 100 meters or more, and the drilling device used for this purpose which, amongst other things, has to have a tripod directed obliquely downwards in order to guide the train of rods, is large and weighs at least two tons because the weight of the drilling machine serves partially as an abutment for the force serving to push the train of rods forwards.
It is precisely when connecting to buildings, however, that a particular problem is encountered because, in this case, the section of main supply conduit, which usually extends under a road, has to serve, by means of the secondary branch conduit, a building disposed close to the road.
For this reason, it is still customary to lay these branch conduits for buildings in conventional manner by the excavation of a trench.
Now, it has already been indicated that this technique has disadvantages requiring in particular, heavy earth-moving and subsequent reinstatement works.
It would therefore be desirable to have available for these and similar applications, a solution which requires only an extremely small hole in the ground surface and not a trench generally over the greater part of the connection conduit to be laid.
The currently-known drilling methods in which a train of rods is driven underground obliquely are in fact not suitable for forming branch conduits for buildings.
With this method, it is certainly possible to guide the drilling quite precisely. However, it is not possible to work as close as would be desirable to the main conduit to be connected without at the same time risking damage to this conduit during drilling.
Moreover, the borehole has to be positioned underground at a point having a relatively large lateral offset relative to the main section. The drilling machine would therefore be installed on the opposite side of the road which would involve closing the whole of one side of the road or, since the resulting lateral distance would, as a general rule, not be sufficient, it would also be necessary to close off the land opposite the building to be connected. The resulting demolition and reinstatement works alone are conducive to the exclusion of this technique.